LED chips deliver more colours despite low profile, low footprint

Delivered in an industry-small form factor, the SML-D22MUW, is a compact, low profile, two-colour chip LED from Rohm.

Rohm claims that it is the industry’s smallest class (1608 size) of two-colour chip LEDs. In addition to their breakthrough size the SML-D22MUW features a special design that improves reliability along with a backside electrode configuration that supports high-resolution displays.

In recent years, chip LEDs have been increasingly used for numerical displays in industrial equipment and consumer devices. Conventional numerical displays use a single colour to indicate numbers, but there is a growing need to change the colour to make it easier to recognise abnormalities. However, this typically entails using two separate LEDs, which doubles the mounting area along with development costs, or opting for a standard two-colour LED that also increases board size.

Proprietary technologies and processes allowed Rohm to integrate two chips in the same package size as conventional single-colour LEDs, making it possible to emit multiple colours in a smaller footprint. Board space is reduced by 35 per cent over standard 1.5 x 1.3mm two-colour LEDs, contributing to thinner displays. Counter-measures have been adopted to prevent solder penetration within the resin package to ensure greater reliability.

In addition to element miniaturisation, the SML-D22MUW leverages PicoLED mounting and wire bonding technologies to mount two chips (red and green) in a compact 1.6 x 0.8mm package. This is the same size as conventional single-colour LEDs, says Rohm.

The close configuration of colour elements results in excellent colour mixing properties, claims Rohm, making it possible to produce not only red and green colours, but a number of intermediate colours as well.

A stopper, or resist, is used before the gold plating process to block the gold pattern (that features good wettability). This prevents solder penetration into the resin, eliminating failures due to short circuits and contributing to reliability.

Rear electrode configuration supports high-resolution display. An electrode design allows mounting in narrow spaces, enabling high-definition display in dot matrix and other applications.


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